Qt apps, like kid3-qt, which uses legacy icons "document-*.png", show them as normal document icon under Yaru theme

[Amr Ibrahim]

Qt apps, like kid3-qt, which uses these legacy icons:

document-open.png
document-open-recent.png
document-save.png
document-save-as.png
document-revert.png
document-import.png
document-export.png

The icons are all shown as the same normal document icon under Yaru.

Qt apps only have a problem with legacy icons starting with "document-*" and all other legacy icons are inherited from Humanity under Yaru.

Is there a general solution to force Qt apps to choose the closest icon name from Yaru or Humanity?

Should this bug be issued against upstream Qt?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dmitry Shachnev (mitya57)]

When an icon is missing (e.g. document-open), Qt first falls back to splitting the name by dashes and taking the first part of it (document). Only then it falls back to parent icon themes (Yaru → Humanity). So for all document-* icons it uses document.png from MimeTypes context.

Doing it vice versa would fix the bug. However, the specification explicitly tells us to behave as Qt currently does: https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html#guidelines

> if the more specific item does not exist in the current theme, and does exist in a parent theme, the generic icon from the current theme is preferred, in order to keep consistent style.

Another potential fix would be ignoring the MimeTypes context. The specification says that fallback happens “for all contexts other than MimeTypes”. However currently Qt’s icon loader does not take contexts into account at all. So fixing it in Qt would be difficult.

I have just pinged the Yaru theme maintainer, let’s hope the fix from Yaru will land in Ubuntu soon.

[Amr Ibrahim (amribrahim1987)]

Just a bit of context:
Symbolic action icons are the de-facto in a GNOME environment, full-colour icons are legacy, that's why Yaru theme didn't originally have any "legacy" full-colour action icons as its original author refused to do so.
The recent addition of the coloured document-*.png icons in Yaru is just a workaround for Qt apps in order not to appear broken under Yaru. And not all full-colour icons will be in Yaru, only the needed document-*.png ones.

[Dmitry Shachnev (mitya57)]

In Focal this is now fixed in yaru-theme 20.04.1.

[Dmitry Shachnev (mitya57)]

Sorry, I had no time and didn't upload a fix for Eoan. Now that Ubuntu 20.04 released, I am no longer interested in Eoan fix.